1. Field of the Invention
The present invention relates to loading and unloading of vacuum chambers while a vacuum is maintained in the chamber. More specifically, the invention relates to a load lock apparatus for loading silicon substrates in a substrate processing platform.
2. Background of the Related Art
Cluster tools which combine numerous substrate processing units in a processing platform have become generally accepted as an effective and efficient concept in advanced microelectronics manufacturing. A cluster tool generally refers to a modular, multi-chamber, integrated processing system. It typically consists of a central wafer handling vacuum chamber and a number of peripheral vacuum process chambers. The silicon wafers go through a set of process steps under vacuum in the various process stations without being exposed to ambient conditions. The transfer of the wafers for the processes is managed by the wafer handling vacuum chamber which is also maintained under vacuum conditions. Cluster tools offer significantly higher yields on account of lower defect densities. Different types of cluster tools, such as linear or radial, with different types of architecture are possible.
Substrate processing platforms typically include at least two load lock chambers mounted on separate openings in the central wafer handling vacuum chamber for loading or unloading silicon wafers while the vacuum chamber remains under vacuum. The load lock chambers occupy valuable positions on the processing platform which would otherwise be used for additional process chambers. However, two chambers are usually required to maintain continuous operation such that wafers are processed from one load lock chamber while finished wafers are unloaded from the other chamber and new wafers are loaded.
FIG. 1 (prior art) shows a commercially available substrate processing platform offered by Applied Materials, Inc. under the trademark Endura.RTM.. The platform combines vacuum chambers designed to process silicon wafers at low/high pressure vacuum in the range of 10.sup.-3 to 10.sup.-8 torr.
Referring to FIG. 1, silicon wafers in a cassette 10 are introduced and withdrawn from the platform through a first slit valve by a first load lock chamber 12 or through a second slit valve by a second load lock chamber 14. A first robot 16 having a blade 18 is located in a buffer chamber 20 to move a wafer 22 between various chambers 24, 26, 28 surrounding the buffer chamber 20. A second robot 30 is located in a transfer chamber 32 to transfer a wafer 34 between various chambers 28, 36 surrounding the transfer chamber 32. The buffer chamber 20 and the transfer chamber 32 are connected through two common chambers 28. It is understood in the art that a wafer may be processed or cooled in one or more chambers for any number of times in any order to accomplish fabrication of a desired semiconductor structure on the wafer. A microprocessor controller 38 and associated software is provided to control processing and movement of wafers.
Attempts to connect two or more load lock chambers to a single slit valve in a processing platform have been unsuccessful. Such an apparatus must have internal valves large enough for the transfer of entire cassettes of wafers. Large valves are difficult to seal when the load lock chamber is open to the atmosphere and is mounted on a chamber that is under high vacuum.
It is an objective of the present invention to provide a load lock apparatus for mounting two load lock chambers on a single slit valve in a substrate processing platform. It is a further objective of this invention to provide a large valve in a load lock chamber which will remain sealed when the load lock chamber is mounted on an opening in a vacuum chamber under high vacuum conditions.